NON-THERMIONIC CATHODE FOR HIGH POWER, LONG PULSE, LONG LIFETIME MAGNETRONS

In conventional microwave tubes, electrons are supplied by tunneling from specially prepared cathodes that are heated to high temperatures (>1000C),  Total current (and tube power) is limited by cathode temperature with higher power possible only with higher temperatures or more exotic cathode materials.  Operating at these temperatures results in reduced cathode lifetime and fragile tubes.  Since the cathodes must be heated continuously even in low duty cycle pulsed operation, large support power systems and cooling are required. Our goal is to develop a cathode structure which operates at ambient temperature, a cold cathode, in which the electrons are produced by field emission from unheated micro-fibers covering the cathode surface.  If the tips of these fibers are sharpened, the field is considerably higher than the average and large electron emission results.  Careful fiber construction along with conditioning and specialized coatings reduces or eliminates outgassing and plasma formation.  The electron emission is controlled by a voltage between the cathode and a transparent grid so that R.F. can be gated without the need for and external modulator. This  approach will result in microwave tubes of higher power, longer lifetime, greater ruggedness and reduced complexity than conventional systems. BENEFIT: Success in this effort will result in significant power generation capability in conventional and high power microwave tubes.  Substantial savings in weight and complexity accompanied by lifetime enhancement will be accomplished by elimination of conventional heated cathode technology.)